1. Field of the Invention
The present invention is directed to ballast systems for use with fluorescent lighting systems and more particularly to circuitry for turning on and off electronic ballasts requiring only low power drain as opposed to the typical high power surges, usually found in this environment.
2. Background Art
It has been determined that when an electronic ballast is first energized from an alternating current power line, a very large surge of current quickly occurs. This large and usually excessive current flow is because two large (such as 100 microfared) filter capacitors are discharged. With a typical electronic ballast fully discharged (having an ESR of 1.21) a surge current of 50 amps may be experienced.
In those environments where there are particularly a large number of ballasts operated at the same time, for example, 30-36, this may represent capacitance from 6,000 to 7,200 mf. Thus, in such an environment when the lamps are turned on it will cause a current surge of over 100 amperes. Usually a high powered expensive relay must be used to handle such an initial load. The momentary surge current may very well cause a momentary dip or drop in line voltage. This line voltage drop could then adversely affect other equipment on the same branch circuit particularly those items that are critical of such brief changes such as computer terminals and the like. A number of attempts have been made over the years to provide a solution to the aforementioned problem. A representative of such solutions have been noted and set forth in the following U.S. Patents.
U.S. Pat. No. 4,042,855 which issued to Buenzii, Jr. teaches a ballast arrangement with a central rectifying control panel in the high frequency inverter. Included in the high frequency inverter is a low energy switch controlling the operation of the high frequency transistor ballast. A low voltage current limiting remote on off control capability is provided at low cost through a secondary winding on a transformer included in the inverter circuit.
U.S. Pat. No. Re. 31,758 which issued to Nilssen teaches an inverter means wherein are included feedback means operable to prevent premature transistor conduction and a capacitor connected between the collector and inverter transistors operable to restrain the rate of change of transistor collector voltage to minimize energy dissipation. This patent teaches an inverter wherein there are included sensing means and frequency control input means. Sensing means being responsive to the magnitude of the DC voltage to provide an input to the frequency controlling circuitry to cause the magnitude of AC current to remain relatively constant regardless of the periodic variations in magnitude to the DC voltage.
U.S. Pat. No. 4,999,546 which issued to Koda et al teaches a starting device for fluorescent lamp and causes the frequency of the pulses of fixed duty ratio to be adjusted to enable the high voltage applying means of the inverter to apply a high voltage of a frequency proper for pulses to the discharge tube and effect efficient and stable start of the discharge tube, thus providing some power reduction. The patent also teaches sequential starting of the individual tubes in the multiple lamp facility to reduce the power requirements.
To overcome the problems outlined above, the present invention solves the problem by keeping the included large filter capacitors in the ballast fully charged at all times, thus control of the fluorescent lamps is accomplished by starting and stopping the high frequency oscillator means. When the lamp is off a low trickle current is required from the AC line.